(1) Field of the Invention
The present invention relates to solid oxide fuel cells and methods for manufacturing the solid oxide fuel cells.
(2) Description of the Related Art
Conventionally, solid oxide fuel cells (SOFCs) are classified into the following types: so-called electrolyte-supported cells, wherein a plate-like electrolyte is used as a support, and a anode is formed on one surface of the electrolyte, and an cathode is formed on the other surface of the electrolyte (for example, Japanese Unexamined Patent Publication No. 2004-055194); so-called electrode-supported cells, wherein one of the anode or cathode is used as a support, and the electrolyte and other electrode are formed in order on the support (for example, Japanese Unexamined Patent Publication No. 2006-253071); and the like.
However, these electrolyte-supported and electrode-supported fuel cells are susceptible to cracking because the electrolyte or the fuel or cathode used as a support is not strong enough. For this reason, so-called metal-supported cells are available, wherein a metal substrate is used as a support, and a anode, an electrolyte, and an cathode in paste form are applied to the metal substrate and sintered (for example, Japanese Unexamined Patent Publication No. 2005-174664).
However, because fuel cells of this type generate power by supplying gases separately to the anode and cathode, the electrolyte that defines the boundary between these electrodes must be dense so as to prevent the passage of the gases. Examples of methods for forming such dense films include a method wherein an electrolyte is applied by screen printing and sintered at a high temperature of about 1400° C. When an electrolyte is formed at such a high temperature, however, the support substrate that is typically made of a metal is subject to thermal damage such as oxidation, deformation, and the like. To overcome this problem, methods for forming films at low temperatures, such as CVD and the like, have been proposed, but these methods have suffered from low yields and high costs.
Accordingly, an object of the present invention is to provide solid oxide fuel cells that exhibit improved strength and are capable of preventing thermal damage.